As is well known, a combine harvester includes a large tank that receives clean grain following its separation from contaminants and low-value crop plant parts in the operative parts of the machine.
This clean grain tank can hold a substantial amount of grain, but despite this the storage capacity of the machine is considerably less than the quantity of grain that is harvested from a typical field.
In consequence it is necessary to empty the grain tank periodically while a combine harvester works to harvest a field. It is however for various reasons (including the inefficiency associated with interrupting harvesting activity) not desirable to halt the combine harvester while unloading of grain from the grain tank takes place.
Instead it is commonplace for a tractor to tow a large grain trailer alongside a combine harvester, and for transfer of the grain from the combine harvester to the trailer to occur while the two vehicles travel adjacent one another at the same speed in a field.
A combine harvester typically is equipped with a grain unloading spout that is connected to the clean grain tank. The spout includes a swivel so it can be moved, horizontally in most combine harvester designs, from a stowed position recessed within the combine harvester to a protruding deployed position in which it overlies the open upper side of the grain trailer when unloading of the grain tank is required. Following completion of the unloading step the spout is returned to its stowed position so as not to present a hazard as the combine harvester continues to move.
In order to avoid halting of the combine harvester movement of the unloading spout between the stowed and deployed positions is effected using a powered actuator. As a result the driver of the combine harvester can command deployment and stowing of the unloading spout, using appropriate cab-mounted controls, without leaving the cab or even slowing the combine harvester during harvesting activity.
The unloading spout in a prior art combine harvester is a pipe including e.g. a 90° elbow adjacent a flange including a swivel via which the spout is secured covering an aperture formed in the clean grain tank. A hydraulic actuator interconnects, via respective pivotable connections at each end, the wall of the unloading spout and a part of the combine harvester that is fixed relative to the clean grain tank.
Energising of the hydraulic actuator in one prior art arrangement so it contracts causes the unloading spout to move from the stowed position to the protruding position; and energising the actuator so it extends (or de-energising the actuator if it is spring-biased) causes movement of the unloading spout in the opposite direction, towards the stowed position.
In another known combine harvester an unload tube swings open when a cylinder is extended; and it swings to its storage position when the cylinder is retracted.
The first of these types of prior art arrangement is summarised in FIG. 1, which shows an unloading spout assembly 10 of which an unloading spout is constituted primarily by a hollow metal (e.g. cast/metal sheet) unloading tube 11 formed to include an approximately 90° unloading elbow 12 as illustrated.
At one end the unloading tube 11 terminates in a circular first flange 13 including a swivel bearing that is not visible in FIG. 1. The first flange 13 is secured in mating relationship with a tank flange 14 defining the boundary of a circular opening formed in the top side of a clean grain tank 16 of a combine harvester. The circular first flange 13 and the tank flange 14 are rotatably captive one relative to the other with the swivel bearing acting between them. As a result the unloading tube 11 may be swung essentially horizontally from the stowed position illustrated in FIG. 1 to a deployed position in which it protrudes outwardly from the top of the clean grain tank.
The unloading tube 11 is stabilised at its upper end by a stabiliser rod 17 that is fixed at one, lower end to the unloading tube 11 by way of a boss 18 and is journalled in a support bearing at its free, upper end.
The support bearing is mounted inside a horizontally extending, hollow beam 19 that overlies the unloading tube 11. Hence the support bearing is not visible in FIG. 1.
The support bearing permits rotation of the rod 17 about an axis that generally coincides with the axis about which the unloading tube 11/elbow 12 swivels relative to the tank flange 14, thereby bracing the unloading tube 11 against lateral forces that otherwise would cause uneven loading of the swivel bearing during movement of the unloading tube between the stowed and deployed positions described.
At its otherwise free, cranked end unloading tube 11 terminates in an end flange 21 that is bolted about its periphery to a further circular flange 22 forming one end of a hollow unloading tube extension 23. The unloading tube 11 or the unloading tube extension 23 may include a powered crop-conveying arrangement such as an auger or a belt. Unloading tube extension 23 extends the length of the cranked part of unloading tube 11 and is of sufficient length as to overlie the interior of a towed trailer running alongside the combine harvester when the unloading tube 11 adopts its deployed position. As a result grain or other crop expelled from the clean grain tank 16 via the unloading tube 11 passes along the unloading tube extension 23 and into the trailer.
Movement of the unloading tube 11, and hence unloading tube extension 23, between the stowed and deployed positions is effected in a powered manner by an actuator piston 24 which typically is hydraulically operated. One end 26 of the actuator piston 24 is secured by way of a pivot mounting to the unloading tube 11. The opposite end of the piston 24 is secured by way of a similar pivot to a part of the combine harvester, such as the vehicle frame, that is fixed relative to the clean grain tank 16.
As a result of this arrangement powering of the piston 24 to contract causes movement of the unloading tube 11 and extension 23 from the stowed to the deployed position described; and powering of the piston 24 to extend causes reverse movement, from the deployed to the stowed position. As noted however other arrangements, including those in which e.g. extension of a piston causes movement of an unloading tube to a deployed position and contraction of the piston causes stowing of the unloading tube are known.
The described prior art unloading spout arrangement suffers several disadvantages the first of which is that the transmission angle between the actuator piston 24 and the unloading tube 11 alters as the unloading tube 11 moves between the stowed and deployed positions. This in turn means that the actuator force acting on the unloading tube 11 and extension 23 is not constant.
This is illustrated in FIG. 2, in which the actuator force lever in mm (i.e. the perpendicular lever arm in mm, corresponding to the amount of torque that can be generated with a given force) (y-axis) is plotted against the length of the actuator in mm at points between the fully stowed and fully deployed positions.
It is apparent from FIG. 2 that the force lever applied by the actuator piston 24 is not constant, and is lower at the start and end of its motion than in a middle zone of movement. This in turn means that in order to achieve an acceptable average force lever value the actuator piston must in effect be over-specified with the result that the cost, size, weight and power consumption of the actuator piston are unacceptably high.
Also a special reaction bar 25 is needed for heavy duty unloading tubes to compensate for the high force the actuator generates. The reaction forces resulting from operation of the actuator in such circumstances can distort the shape of the grain tank.